1. Technical Field
The present invention relates generally to composite, lightweight, rigid, structural panels formed of resinous material and to a process for forming the same; and, more particularly, to a process for rigidizing a non-structural, flexible, open cell, reticulated or semi-reticulated, foam sheet formed of resinous material, such, for example, as urethane, polyurethane, or the like, and to rigid structural composite foam products produced thereby. In one of its important aspects, the invention finds particularly advantageous use in rigidizing commercially available, non-structural, flexible, open cell foams of the type preloaded with dielectric and/or magnetic particles distributed throughout the open cell foamed structure for use as electromagnetic wave absorbers.
2. Background Art
Prior to the advent of the present invention, numerous open cell, reticulated or semi-reticulated, non-structural foams have been commercially available; and, such foams have been used for a number of non-structural purposes. For example, one common use of such foams has been as an electromagnetic wave absorber; and, to this end, the flexible, non-structural, open cell foam sheet material has served as a matrix-like support for dielectric and/or magnetic particles distributed throughout the open cells of the foam sheet. Unfortunately, while such products have been highly effective as electromagnetic wave absorbers, they have all been characterized by their inability to function as a load-bearing structural element. Indeed, such open cell, non-structural, foam products have been highly parasitic in nature, requiring the use of a separate rigid structural support to which the open cell foam sheet can be laminated and wherein the open cell foam sheet and its matrix of discrete dielectric and/or magnetic particles contributes to the thickness, bulk and weight of the rigid support while providing no enhancement of the load-bearing characteristics thereof. Moreover, such open cell foam products require separate laminating techniques, materials and operations to enable their attachment to a rigid structural support; and, once laminated thereto, are prone to damage and/or contamination during use as a result of exposure of the surface of the flexible open cell structure to environmental contaminants and/or conditions.
Because of the foregoing disadvantages, numerous efforts have been made to rigidize such foam sheets, all without success prior to the present invention. Such efforts have involved, for example, squeezing or compressing the foam sheet material and placing the thus compressed material in a liquid rigidizer bath so that upon expansion to the original noncompressed state, the foam sheet material will hopefully soak up or absorb the liquid rigidizer, much like a sponge. This approach has, however, proven unsuccessful and suffers from numerous disadvantages. For example, squeezing or compressing the open cell foam sheet tends to break down the cell walls and thus damages the foam and its integrity as a matrix-like support for dielectric and/or magnetic particles. Moreover, the process has not resulted in a uniform dispersion of the liquid rigidizer throughout the open cell non-structural foam sheet; and, consequently, the resulting product does not have uniform strength or load bearing characteristics. Moreover, this process does not readily lend itself to formation of rigidized products having any desired non-planar configuration.
Yet another approach has involved efforts to force the liquid rigidizer under pressure into the non-structural open cells of the foam sheet from opposite faces thereof. However, this process has invariably produced a product wherein the rigidizer not only is not uniformly distributed throughout the open cell foam sheet; but, moreover, wherein the central region of the sheet has little or no rigidizer therein.
Numerous somewhat related processes and/or equipment for reinforcing resinous products are described in prior patents. For example, U.S. Pat. No. 3,989,781-Chant discloses a process for producing a laminar product including a resin impregnated fibrous reinforcing material. In this process, the patentee contemplates impregnating a foam sheet with a curable thermosetting resin, positioning a fibrous reinforcing layer on one or both faces of the impregnated foam sheet, positioning the adjacent laminations thus formed within a closed mold, and introducing a resinous expandable polyurethane foam into the closed mold so that expansion of the polyurethane foam causes the resin impregnated in the foam sheet to be expressed out of the foam sheet and into the adjacent fibrous reinforcing lamination(s) so as to form a composite laminar product having: (i) at least one rigid lamination of fibrous reinforced hardened thermosetting resin; (ii) a rigid layer of compressed foam impregnated with hardened resin; and (iii), a layer of polyurethane foam. The patentee suggests (Col. 2, 11. 50-51) that the rigid resin in the fibrous reinforcing layer(s) forms a hard rigid skin on the polyurethane foam.
In U.S. Pat. No. 3,341,640-Rosencarntz, the patentee discloses a process for forming pad bodies such as seats or backs for furniture, mattresses, cushions, or the like. In this process, the patentee employs a core of foamed material such as polyurethane and, particularly, polyurethane polyethers, which is positioned on upwardly projecting pins in the bottom of a mold cavity while the lid of the mold is provided with similar downwardly projecting pins dimensioned to touch, but not penetrate, the core. Thereafter, a foamable rubber material is introduced into the mold in surrounding relation to the polyurethane core and allowed to cure so as to form a composite product having a central polyurethane core and an outer coating of foamed rubber or the like wherein the outer coating includes depressions and/or openings in the regions occupied by the mold pins.
U.S. Pat. No. 2,770,864-Weese is of general interest for its disclosure of a method for producing a molded self-rising cellular concrete or like cellular material of any desired configuration wherein the material is placed within a mold-like cavity and covered by a perforate screen or lid, thus enabling the material to expand through the perforations and permitting the operator to redistribute the excess material to regions where the material has not filled the mold cavity.
A somewhat similar process is disclosed in U.S. Pat. No. 4,239,564-Krumweide, wherein the patentee forms a uniform, low density, constant thickness, foam material sheet on a structural surface by positioning a screen in a plane parallel to and spaced above the structural surface, and then spraying or otherwise applying the foam material through the screen to substantially fill the space between the structural surface and the screen. The screen is thereafter stripped from the product, leaving a uniform, constant thickness, foam lamination on the structural surface which is bonded thereto during curing.
Other patents of interest include: U.S. Pat. No. 3,047,888-Shecter et al [a mattress or other laminar product having a central lamination of high hysteresis, low recovery rate, urethane foam, and outer facing laminations of resilient foam rubber or urethane]; U.S. Pat. Nos. 3,917,547-Massey, 3,993,608-Wells, 3,996,654-Johnson, and 4,362,778-Andersson et al [patents which disclose various methods and/or products wherein particles, spheres or the like are distributed throughout the foam material]; and, U.S. Pat. Nos. 4,208,696-Lindsay et al, and 4,258,100-Fujitani et al [wherein electrically conductive laminar webs are provided containing a centrally conductive layer which, in the Lindsay et al patent, comprises a latex or resin coated scrim or open cell foam containing carbon particles, to which are bonded outer layers of thermoplastic polymers or fibrous material].
However, none of the foregoing processes and/or equipment disclose a system for rigidizing a non-structural, open cell, reticulated or semi-reticulated foam by forcing a flowable foamable resinous material into and through the open cell foam structure.